Shape recovery and reprocessable polyurethanes crosslinked with double decker silsesquioxane via Diels-Alder reaction

Abstract

Abstract In this work, a novel organic-inorganic polyurethane thermoset crosslinked with a difunctional polyhedral oligomeric silsesquioxanes (POSS) was synthesized via Diels-Alder (DA) reaction. First, a linear multi-segmented polyurethane with furan rings in the main chain (PU–F) was synthesized via the step-growth polymerization of 4,4′-diphenylmethane diisocyanate (MDI) with poly(tetramethylene ether glycol) (PTMEG) and 2,5-furandimethanol. Second, 3,13-dimaleimido octaphenyl double decker silsesquioxane (3,13-dimaleimido DDSQ) was synthesized and used as the crosslinker of the linear PU-F. By adjusting the feed ratio of the difunctional POSS macromer (i.e., 3,13-dimaleimido DDSQ) to PU-F, the organic-inorganic PU thermosets (denoted DAPU-DDSQs) with variable densities of crosslinking were obtained. It was found that the DAPU-DDSQs were microphase-separated and that POSS cages were aggregated into the spherical microdomains, the sizes of which were 20–40\xa0nm in diameter. It was demonstrated that the crosslinking in the DAPU-DDSQs had two aspects of contribution: i) the chemical crosslinking with D-A adducts between 3,13-dimaleimido DDSQ and PU-F and ii) the physical crosslinking with POSS microdomains via the aggregation of POSS cages. The DAPU-DDSQs displayed the improved thermomechanical properties with increasing 3,13-dimaleimido DDSQ incorporation. Owing to the formation of crosslinked structures, the DAPU-DDSQs displayed excellent shape memory properties. More importantly, the DAPU-DDSQs displayed the reprocessing (or recycling) properties at the temperature of retro DA reaction. The reprocessing properties of the DAPU-DDSQs can be utilized to re-edit the original shapes of shape memory PUs.